B21C-0450
Manganese Influences Carbonate Precipitation in a Laminated Microbial Mat

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Megan Krusor1, Sharon L Grim2, Dylan Wilmeth3, Hope Johnson4, William Berelson3, Bradley S. Stevenson5, Blake W. Stamps5, Frank A Corsetti3 and John R Spear6, (1)University of California Davis, Davis, CA, United States, (2)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (3)University of Southern California, Los Angeles, CA, United States, (4)California State University Fullerton, Fullerton, CA, United States, (5)University of Oklahoma Norman Campus, Norman, OK, United States, (6)Colorado School of Mines, Golden, CO, United States
Abstract:
Investigating mineralization within modern microbial mats informs our interpretation of ancient microbialites and the mineralization process. Microbial mats in Little Hot Creek (LHC), California contain 4 distinct layers with different microbiota. Each layer of the mat is supersaturated with regard to calcium carbonate (CaCO3), which increases with depth. Total organic carbon decreases with depth through the mat.

We used 13C-labeled bicarbonate incubations of each mat layer to calculate growth rates of organic carbon and CaCO3 within the mat. Incubations were also amended with Mn or Mg to test their effect on rates of CaCO3 and organic carbon formation. The Mn-amended top layer increased CaCO3 precipitation and organic carbon growth. Mn increased organic carbon production in the lowest layer to a lesser extent, but not growth of CaCO3. Mn addition had no effect on growth rates in the two intervening layers. Mg amendment stimulated only organic carbon formation in the top layer, with little to no effect on the lower layers or overall CaCO3 formation.

We attribute the elevated CaCO3 precipitation noted after Mn addition to increased oxygenic photosynthetic activity. Oxygenic photosynthesis requires Mn as an enzyme cofactor and promotes carbonate precipitation. We propose that the phototrophic community was responsible for most of the CaCO3 precipitation in the upper layer. Phototrophs gradually moved upwards for optimal access to sunlight, and as the mat grew, “tenant” microorganisms inhabited the lower carbonate layers while the “builders” remained on top. The relatively constant percentages of inorganic carbon below the top layer combined with observed minimal CaCO3 precipitation under laboratory conditions suggest that additional research into potential metabolisms that impact carbonate formation would be informative. These results improve our understanding of the linkages between microbial metabolisms, carbonate precipitation in microbial mats, and the potential of microbial mats to mineralize.

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